A sail may be considered a thin cambered airfoil shaped surface where the maximum aerodynamic efficiency is obtained when functioning as a laminar air flow device. The present invention involves the use of laminar air flow control means to improve sail performance.
U.S. Pat. No. 2,971,488 shows a sailboat with one long line of single holes disposed along the rear or trailing edge of the sail and just ahead of a hinged boom and sail flap arrangement that terminates the trailed edge of the sail. This single line of relatively large holes is intended to prevent turbulence at the trailing edge of the sail.
U.S. Pat. No. 1,864,964 shows a sail boat wherein fabric scallops or pockets are provided near the leading edge of the sail adjacent the mast. These pockets are directed to one side of the sail or the other by means of ropes under control of the helmsman. The stream caused by the pockets deflects the air stream away from the leeward side of the sail to increase the negative pressure at that area adjacent the front or mast zone of the sail. In FIG. 6 a parachute is shown having a double circumferential row of large apertures. Diagonally disposed pairs of two holes are thus formed, each sharing a common hole, so that the converging ends of each hole row are not spaced. The apertures form horizontal streams that deflect the normal air current to a path further away from the parachute canopy than would be their path if the apertures were absent.
Canadian Patent No. 701,079 shows rows of orifice jets formed over substantially the entire surface of the sail. The orifices direct the air flowing therethrough tangentially along the convex or leeward side of the sail. The orifices are produced by having the down wind edge of the orifice tight and the upward edger loosely crowned and positioned to the leeward side of the sail. These slots are all intended to act as reactive jets. The large orifices produce jets of air similar to slots like those between a wing and trailing edge flaps without creating laminar-type air flow.
U.S. Pat. No. 3,776,170 shows a sail provided with short rows of closely spaced holes, with the axis of the rows converging and being inclined at an acute angle to the path of the free air past the sail. The converging ends of the individual rows are relatively widely spaced and the rows are arranged in an array from the head to the foot of the sail. The angle between the axis of each row of holes and the direction of the free air flow path is alternated along the array from a positive to negative angle. The rows of holes, in turn, produce a row of discrete air jets on the convex, low pressure side of the sail, forming aerodynamic "fences." These fences present a partial obstruction to the flow of the air past the sail, causing the air to form twisted streams when spilling over the aerodynamic fences. These streams form continuous, helical trailing vortices that mix the free air stream with the slower moving boundary layer of the air next to the convex surface of the sail. The resulting mixing action continually energizes the boundary layer of air, thus preventing stall and improving the driving force of the sail. The principle is said to be also useful in the control of parachutes and other thin air foils.
U.S. Pat. No. 3,152,782 shows a parachute wherein frusto-conical nozzles terminating in tubular extensions are formed in staggered circumferential rows around a specially provided torodial bulge adjacent the lower portion of the parachute canopy. These nozzles are provided to maintain a constant turbulence around the canopy bulge. The nozzles form interlaced or crossing rows of three, each row of three sharing a common nozzle, so that the rows of three have no gap between them at the converging end of the rows.
None of the above references describe a device which provides apertures that maintain laminar-type air flow over the entire surface of a sail. None of these references describes a device designed to "bleed" the high energy windward or concave side air to the leeward or convex side of a sail to replace the boundary layers on both sides of a sail with no laminar flow-type boundary layers down stream of the apertures in the direction of the passing air flow.